That God is love is one of those nice sentiments that even the spiritual-but-not-religious can appreciate. Of course God is love; of course God accepts all people; of course God could never send a person to hell forever; and so on.
I don't disagree with these sentiments, but I think they must be uttered from within the proper context in which they may be seen to be plausible. Taking a look at the the world around us, the thought that God is love may be the last one to come to mind. How can one believe in a God of love in a world like ours, where there is rape and torture and cancer and mass murder? In the face of a world like this, a belief that God is love may seem like nothing more than a nice story a particular species of primate tell themselves to make the hellish travails of their terrestrial existence more tolerable.
But the Christian can make a confident affirmation of the love of God in the face of the evils of the world, and the quotidian spiritual-but-not-religious person cannot, precisely because of the revelation of Jesus Christ. We read in 1 John 4.8-10: Whoever doesn't love, hasn't known God, because God is love. God's love was revealed among us in this: namely, he has sent his only Son into the world, so that we should live through him. This is love: not that we have loved God, but that he loved us and sent his son as an atonement for our sins.
It is through the fact of the Father's sending the Son to give life to the dead, and to atone for the sins of the sinful, that we know that God is love. In the words of T. F. Torrance, [T]he cross . . . tells us that God loves us more than he loves himself (A Passion for Christ: The Vision that Ignites Ministry, p. 14). We are victims of the many evils in the world, that is true. But we know that God is love because he allows himself to be victimized by us -- to suffer for our sake, and because of us -- in order to do us the greatest good we could imagine: that we live forever in a renewed world in fellowship with him.
I believe in a loving God, but not because of sentiment or vague religious intuition. All Christians believe in a loving God because God himself has revealed himself to be loving in this way. Therefore, we can make a firm affirmation of God's love in the face of all evil, none of which can ever undo that great, loving act of salvation accomplished for us in Jesus Christ.